1. Field of the Invention
The present invention relates to a system for monitoring characteristic parameters of a tyre fitted to a vehicle.
In particular, the present invention relates to the possibility of sensing characteristic parameters, such as for example pressure, temperature and accelerations, inside a tyre using a sensor placed inside the tyre itself.
2. Description of the Related Art
A wheel is the connection between the vehicle and the road; it performs the function of providing pneumatic suspension for the vehicle and its load and providing, through the tyre, satisfactory behaviour on the road. The suspension of the vehicle is provided by the volume of compressed air contained inside the wheel.
A tyre comprises an internally hollow toroidal structure formed by a plurality of components, in the first place a textile or metallic carcass ply, the edges of which are attached to at least one pair of annular reinforcing cores known as bead wires, which are circumferentially inextensible and are inserted in two beads each defined along an internal circumferential edge of the carcass in order to anchor the tyre to the corresponding supporting rim.
The carcass ply includes a supporting structure that runs axially from one bead to the other to form a toroidal structure comprising a plurality of textile or metallic cords embedded in a layer of elastomeric material. In tyres of the so-called “radial” type, the abovementioned cords essentially lie in planes containing the axis of rotation of the tyre.
Forming a ring around this carcass are an annular superstructure known as the belt structure, normally made up of one or more strips of rubberized fabric wound on top of each other to define a so-called “belt pack”, and a tread band of elastomeric material wrapped around the belt pack and moulded with a relief design for rolling contact of the tyre with the road. Two elastomeric side walls are also placed on the carcass, in axially opposite lateral positions, each extending radially outwards from the outer edge of the corresponding bead.
In tyres of the so-called “tubeless” type, i.e. those that require no inner tube when in use, the inside surface of the carcass is normally covered with a so-called “liner”, which is one or more layers of elastomeric material impermeable to air. Lastly, the carcass can include other known components, i.e. edges, shims and fillers depending on the particular design of tyre.
A pneumatic vehicle wheel comprises a tyre defining a toroidal cavity and mounted on a corresponding rim, which has a bottom surface provided with a central well and two bead seats against which the tyre beads come into abutment and which are each axially defined between an extreme radial surface (shoulder) in an axially external position and an opposing, axially internal, annular projection which locks the bead on the corresponding seat.
In a “tubeless” tyre, the compressed air is contained between the tyre and the supporting rim. The liner on the inside surface of the tyre keeps the air at pressure inside the tyre. This tyre is inflated through an inflation valve which is usually positioned on the drop centre of said rim.
A tyre of this type is described for example in Patent Application EP928680.
Another way of maintaining the suspension capacity of the tyre is to use an inner tube inserted between the tyre and the rim and inflated with compressed air which is injected into the tube through an inflation valve projecting out through the wheel.
The inner tube, inserted between the tyre and rim, comprises a tubular body expandable to give toric shape. It is generally made of elastomeric material and inflates through an inflation valve.
The inflation valve of the inner tube usually includes a base for attachment to the inner tube and a cylindrical envelope (shank) fixed to the base and containing the mechanism that has to be activated for inflation and deflation operations.
An incorrectly inflated tyre reduces the efficiency of the vehicle: in particular, it causes increased fuel consumption, poorer handling and greater tyre wear, to cite only a few of the most serious drawbacks.
It is therefore of the greatest importance to be able to continually monitor the pressure in the tyres of the vehicle. Also, if it is wished to check the behaviour of a moving tyre, other parameters can be monitored, such as, for example, the accelerations and deformations that take place within a tyre.
U.S. Pat. No. 5,540,092 discloses a system for monitoring the pressure in a tyre comprising a pressure sensing unit and a unit for transmitting an encoded signal to the vehicle on which the tyre is fitted. The transmitting unit may be mounted inside or outside of the tyre. The transfer of this coded signal takes place by inductive coupling between the transmission unit and a fixed antenna. A battery powers this transmission unit.
U.S. Pat. No. 5,562,787 discloses a method for monitoring the conditions of a vehicle tyre, e.g. the pressure and temperature of the air in the tyre. The method uses a programmable self-powered device mounted on the inside surface of the tyre or inserted in the wall of the rim on which said tyre is mounted. The device comprises a power source that can be made active or inactive using a switching device, a sensor for monitoring said information, an integrated circuit, an amplifier and an antenna. A transmitter-receiver located on the vehicle or in a remote position interrogates the programmable self-powered device, which answers with a radio-frequency signal containing the required information. The programmable self-powered device is activated by said remote transmitter/receiver which instructs the switching device to make the power source active.
U.S. Pat. No. 6,217,683 discloses a tyre monitoring device in which a module for monitoring information about the state of the tyre is inserted in the tyre itself and attached to the inside surface of the tyre by a fixing mechanism. This fixing mechanism comprises a fixed part attached to the surface of the tyre carcass, and another part attached to said module. Said first and second parts together keep said module in contact with the inside surface of the tyre carcass. One application of the monitoring system is to measure the tyre pressure. The measurement is transmitted to the outside by radiofrequency signal.
Patent application WO 9929524 discloses a tyre pressure sensor encapsulated in elastomeric material and attached in the toroidal zone of the tyre, preferably in the vicinity of the equatorial plane of said tyre. The sensor is attached to the inner surface of the tyre by an adhesive or is attached by the curing of the elastomeric material during manufacture of the tyre.